Injecting facter into file content - no implicit conversion of Hash into String - puppet

Question

I want to inject some values from facter <prop> into a file content.
It works with $fqdn since facter fqdn returns string.
node default {
file {'/tmp/README.md':
ensure => file,
content => $fqdn, # $(facter fqdn)
owner => 'root',
}
}
However, it does not work with hash object (facter os):
node default {
file {'/tmp/README.md':
ensure => file,
content => $os, # $(facter os) !! DOES NOT WORK
owner => 'root',
}
}
And getting this error message when running puppet agent -t:
Error: Failed to apply catalog: Parameter content failed on
File[/tmp/README.md]: Munging failed for value
{"architecture"=>"x86_64", "family"=>"RedHat", "hardware"=>"x86_64",
"name"=>"CentOS", "release"=>{"full"=>"7.4.1708", "major"=>"7",
"minor"=>"4"}, "selinux"=>{"config_mode"=>"enforcing",
"config_policy"=>"targeted", "current_mode"=>"enforcing",
"enabled"=>true, "enforced"=>true, "policy_version"=>"28"}} in class
content: no implicit conversion of Hash into String (file:
/etc/puppetlabs/code/environments/production/manifests/site.pp, line:
2)
How to convert the hash to string inside the pp file?

Answer 1

If you have Puppet >= 4.5.0, it is now possible to natively convert various data types to strings in the manifests (i.e. in the pp files). The conversion functions are documented here.
This would do what you want:
file { '/tmp/README.md':
ensure => file,
content => String($os),
}
or better:
file { '/tmp/README.md':
ensure => file,
content => String($facts['os']),
}
On my Mac OS X, that leads to a file with:
{'name' => 'Darwin', 'family' => 'Darwin', 'release' => {'major' => '14', 'minor' => '5', 'full' => '14.5.0'}}
Have a look at all that documentation, because there are quite a lot of options that might be useful to you.
Of course, if you wanted the keys inside the $os fact,
file { '/tmp/README.md':
ensure => file,
content => $facts['os']['family'],
}
Now, if you don't have the latest Puppet, and you don't have the string conversion functions, the old way of doing this would be via templates and embedded Ruby (ERB), e.g.
$os_str = inline_template("<%= #os.to_s %>")
file { '/tmp/README.md':
ensure => file,
content => $os_str,
}
This actually leads to a slightly differently-formatted Hash since Ruby, not Puppet does the formatting:
{"name"=>"Darwin", "family"=>"Darwin", "release"=>{"major"=>"14", "minor"=>"5", "full"=>"14.5.0"}}